Electro-chemical deposition processes are used to deposit materials on exposed surfaces of objects. Electro-plating is one well-known electro-chemical deposition process. To plate an object using an electro-plating process, the object and an electrode are placed in a bath of electroplating solution. The electrode is placed in proximity to the object to be plated and a voltage is applied between the electrode and the object. In the presence of the electric field, current flows through the electroplating solution and a chemical reaction occurs, the result of which is the deposition of the plating material on the object. Electro-plating is a commonly-used process for applying a layer of metal to an object.
To increase their lifetime, the interior surface of gun-barrels, such as those used in artillery pieces and tanks, are often coated with chromium using a “flow-through” electro-plating process. In order to coat the interior surface of a gun barrel, a copper electrode (of the appropriate diameter with respect to the center bore of the gun barrel) is inserted into the barrel during plating. Electroplating solution is flowed through the region between the electrode and the barrel while a voltage is applied between the electrode and the barrel. In the presence of the applied voltage, a current flows through the electroplating solution and chromium deposits on the interior surface of the gun barrel.
Conventional hard-chromium is electroplated using electric current of approximately 6,000 amperes. Low-contraction (LC) chromium, however, is highly desirable in many applications, including for coatings of gun barrel interiors. Unfortunately, the plating of LC chromium requires the use of a much higher current—as high as 48,000 amperes. The electric field associated with the electroplating of LC chromium induces a substantial mechanical force between the electrode and the gun barrel. As a result of this force, the electrode can bends to one side and electrically short to the gun barrel. Even if the electrode does not short to the gun barrel, however, the bending effect results in an uneven deposition of chromium on the gun barrel.
In an effort to eliminate bending of the electrode, stand-offs are inserted into the electrode. These stand-offs are installed both radially and axially along the length of the electrode, and provide a mechanical “stop” that helps maintain the separation between the electrode and the interior surface of the gun barrel. While these stand-offs do reduce the bending of the electrode, they interfere with the flow of electroplating solution through the length of the gun barrel. Due to flow effects, such as stagnation and eddying, the stand-offs cause a “shadowing” effect that reduces the plating thickness near the locations of the stand-offs.
Methods and apparatus which mitigate the problems associated with bending of the electrode while reducing the shadowing effect, is therefore desirable.